Rare malignant transformation of struma ovarii into follicular thyroid carcinoma: A case report.

Struma ovarii is a rare monodermal ovarian teratoma primarily composed of thyroid tissue, accounting for 2-5% of all ovarian teratomas. Although generally benign, about 5% may undergo malignant transformation, predominantly into papillary thyroid carcinoma, with follicular thyroid carcinoma being exceptionally rare. A 46-year-old Asian woman presented with abdominal pain. Imaging studies identified a solid-cystic ovarian mass with elevated CA-125 levels. Surgical intervention was performed, and histopathological examination confirmed the malignant transformation of struma ovarii into follicular thyroid carcinoma. Post-operative PET-CT and hormone level assessments showed no residual disease. The patient is currently under regular follow-up. This case illustrates the rarity and diagnostic challenges associated with malignant struma ovarii. It underscores the importance of extensive sampling and a multidisciplinary approach for effective management. Given the lack of standardized treatment guidelines, personalised care and close follow-up are essential, with consideration of aggressive treatment based on risk assessment.